This section provides background information related to the present disclosure which is not necessarily prior art.
Conventional manual transmissions generally have several basic components including a gear set, a clutch, and a gear change (i.e. a manual shift lever). As such, conventional manual transmissions are relatively simple in design, leading to cost savings, increased efficiency, and good reliability. To launch a vehicle and to change gears, the driver engages the clutch, selects a gear, and then releases the clutch while controlling clutch pressure and engine speed. Hence, the operation of conventional manual transmissions can demand considerable driver concentration and coordination. Such operations can also be difficult for inexperienced drivers to master and can cause driver fatigue. In city driving or when driving in heavy traffic, where speeds are low and travel is stop-and-go, conventional manual transmissions can be particularly undesirable because the driver must repetitively shift into and out of gear while balancing the application of the clutch to prevent the engine from stalling. Vehicles with conventional manual transmissions can also experience abrupt acceleration during gear changes, particularly where vehicle speed, engine speed, shift timing, and clutch pressure are not properly judged by the driver. This leads to an uncomfortable, jarring ride for the driver and passengers alike.
To ease driving effort and to increase comfort, automatic transmissions were developed. Automatic transmissions eliminate the need for the driver to manually change gears while operating the clutch and adjusting engine speed. Automatic transmissions also have other desirable characteristics including increased smoothness and decreased noise, vibration, and harshness. However, these benefits come with several drawbacks including increased complexity, increased cost, and decreased efficiency.
The centerpiece of conventional automatic transmissions is a torque converter. The torque converter includes a fluid coupling that transfers the rotational power produced by the engine to other drivetrain components. The key functions of the torque converter are to multiply the torque produced by the engine and to permit slip between the engine output and the other drivetrain components. These functions are inter-related and enable a vehicle to be launched from stop without a clutch and without stalling the engine. Torque converters generally include a housing that is connected to and rotates with an engine output shaft such as a crankshaft. Torque converters further include a cover that abuts the housing to form an internal cavity. A stator is disposed within the internal cavity that redirects fluid flow within the internal cavity to multiply engine torque. A pump is connected to the inside of the housing that circulates fluid within the internal cavity. A turbine is disposed within the internal cavity that is driven by the fluid circulating within the internal cavity. The turbine is then coupled to the other drivetrain components through the gears of the automatic transmission. Some conventional torque converters also feature a lock-up clutch disposed within the internal cavity. The lock-up clutch selectably applies pressure against the housing to rotatably couple the turbine with the housing.
In an effort to create new transmissions that combine the efficiency and cost benefits of the conventional manual transmission with the smoothness and refinement of conventional automatic transmissions, conventional torque converters have been mated with manual transmissions. One such design is disclosed in U.S. Provisional Patent Application Ser. No. 61/915,695 filed on Dec. 13, 2013 and entitled “Manual Transmission With Torque Converter.” This design places the torque converter in series between the clutch and the gear set of a manual transmission. However, in such designs the need for a separate clutch disposed between the engine output and the torque converter remains.